320 gCTENTlFtC NETW^gV 



^escribipg the primitive figure of this substance, Mr. I*,- 

 proceeds to an enumeration and description of those modi- 

 fications, with their varieties, which have been observed by 

 hira, and specimens of which are at present in his cabinet. 

 Twin crystals. After describing twelve modifications, the paper concltfdes 

 with details of those compound crystals usually called 

 macles ; of the still more compound ones, which are formed 

 by the junction of two n\acles; and of the most compound 

 of all, which are macle«: of macles. 

 Castle hill, A description of Castle hill near Newhaven in Sussex, by 



"eu'^in Sussex. I^^"' Warburton, Esq., Memb. of the Geo. Soc* was read. 

 Castle bill is a small circular elevation, composed of nearly 

 horizontal beds, lying above the chalk in the following order, 

 beginning from the most recent:— 1, Sand and rounded 

 flint pebbles. 2, A congeries of oyster shells. 3, A bed of 

 broken bivalve shells, chiefly of the genus Venus, 4, A 

 bed of blue clay, enclosing a seam of martial pyrites 3 or 4 

 inches thick, composed entirely of casts of bivalve and tur- 

 binated shells. 5, A bed of indurated marl, the lower part 

 of which is obscurely slaty, and contains between its laminae 

 leaves apparently of some tree of the willow tribe converted 

 into coal. 6, A seam of coal three or four inches thick, 

 7, Marl, of a sulphur yellow colour, including large crystals 

 of gypsum, 8, Sand. 9) Chalk. 

 A.ccidental A notice respecting an accidental sublimation of silex by 



cfsllS!*'''" Dr. Mac Culloch, Mem. Geo. Soc, was read. A mixture 

 of the oxides of tin and lead was put into an earthen cruci- 

 ble, and covered by another inverted over it :. the mass was 

 exposed to a high heat, and on opening the crucibles the 

 empty part of each of them was found lined with capillary 

 shining crystals, which by the usual raethoda of analysis 

 were proved to be pure silex. 



To Correspondevis. 



I fiind myself again unfortunately obliged to postponemj' 

 answer to A. H. Z. till next month, ^ ?,.;..;• 



